This invention relates to a method and an apparatus for measuring a displacement of one member relative to another, and more particularly to a method and an apparatus for measuring a minute rotational or linear displacement of a rotary or linearly movable member relative to a stationary member.
One known method of measuring a minute rotational angle of a rotary body employs a plurality of gears to mechanically magnify the rotational movement of the rotary body. This method, however, has a disadvantage that the mechanism for carrying out the method is complicated in structure and large in size. Another disadvantage is that the backlash, pitch error or runout of the magnifying gears causes errors in the the result of measurement.
Accordingly, it is one object of the invention to provide a method and apparatus for measuring a minute rotational angle of a rotary body, which is relatively simple and enables accurate measurement.
For measurement of a minute linear displacement such as strain caused by a stress in a body, there are known various methods such as the moire fringe method and the laser interference method.
Another object of the invention is to provide a method and apparatus for measuring a minute linear displacement of an object, which is relatively simple and enables accurate measurement.
The invention will be described in detail with reference to the accompanying drawing.